A new mine on the West Coast's Denniston Plateau is unlikely to boost the declining industry's job numbers for several years, its owner says.

Conservation Minister Nick Smith announced on Wednesday that Bathurst Resources could go ahead with plans for an open cast mine near Westport.

The Department of Conservation (DOC) granted the Australian company an Authority to Enter and Operate (AEO), allowing initial site work to begin.

Bathurst Resources confirmed the mine would operate under reduced production until low international coal prices recovered.

Spokeswoman Sam Aarons said the mine was expected to employ about 200 people at full production, but "half a dozen guys" only would be needed for basic construction work.

That work could begin as early as July 1, and would involve initial site preparations including roading and water management.

As part of the DOC agreement, Bathurst will have seven years to pay $22 million in compensation, which has been tagged for pest and predator control in the Heaphy River catchment and the Denniston Plateau, plus historical projects on the plateau.

Parliamentary Commissioner for the Environment Jan Wright yesterday released an update on her 2010 report on mining on the conservation estate.

Contrary to her recommendations, Parliament passed legislation which allowed decisions on access to conservation land to be made jointly with the minister of energy and resources.

Wright said the change undermined the role of the conservation minister as "guardian of the conservation estate". She said she was not against all mining on conservation land, provided conservation took precedence.

"The greatest threat to our conservation estate is not mining, but introduced pests. There is potential for a win-win, if mining companies pay for substantial pest control."